Mississippi's personhood amendment, where anti-choicers tried to give fertilised eggs the same legal status as your average adult male, has thankfully failed. But while the short-term efforts to give single-cell citizens more rights than adult women may have faltered, pro-lifers aren't giving up. There will certainly be more state personhood amendments in the future, and now congressional Republicans want to take the plan national. So, despite the failure of the Mississippi bill, pro-choicers still need to be vigilant – not just about the law, but about the small cultural shifts that pro-lifers are pushing.

Anti-choice activists aren't stupid (they're wrong, but they're not stupid). Over the past few decades, they've realised that if they can frame reproductive rights as being about saving babies' lives, they've got a winning case – after all, who doesn't like babies? What anti-choicers are actually hostile to are changing gender roles and the increased freedoms and liberties that have been afforded to women by the right to determine the number and spacing of their children. Unfortunately, those freedoms and liberties are wildly popular in the United States. Women like having rights. Women like having sex for pleasure. Women like going to school. Women like being able to work and have children, or have the option of choosing to be a stay-at-home parent rather than being forced or coerced into it. Women like marrying someone they choose, not someone they were accidentally impregnated by.

And we're all better for it. Since the advent of the birth control pill, and since feminism has attempted to position women's rights as basic human rights, more American women are attending colleges; the pay gap is narrowing; divorce rates have gone down; teen birth rates have gone down; both men and women spend more time with their children than in the homemaker heyday of the 1950s and 60s; and fewer children live in poverty than they did in the Leave It to Beaver era. Marriages that are more gender-egalitarian, and which involve women with higher education levels and incomes, tend to last longer and be happier. And 98% of American women will use birth control at some point in their lives.

These are not coincidences. Reproductive rights have been good for men, women, children, families and society.

But women's rights have been bad for anyone who thinks that the only option for women should be to stay home and raise as many children as God gives her. That, obviously, is not the majority of the American public, as evidenced by what the American public actually does. But it is the majority of the American pro-life leadership (which, of course, is distinct from individual voters who identify as pro-life).

For them, the focus on abortion was a good starting point – ending a pregnancy is, for many people, a morally complex issue, and anti-choicers were easily able to stake out the "you're a baby-killer" side. They successfully shifted the conversation to the rights of the fetus, rather than what it means for women to be legally compelled to carry a pregnancy to term. They sold many of us on the idea that an embryo or a fetus is the moral equivalent of a baby – that a fetus is, in fact, a baby, and terminating a pregnancy at 6 weeks is the moral equivalent of killing a three year old. A solid half of Americans now consider themselves pro-life, and significantly more than that believe that abortion is immoral.

But abortion isn't the only thing enabling women to have sex without tacitly agreeing to carry a pregnancy for nearly 10 months and then raise a child. Birth control also does that, and is used far more frequently than abortion. Of course, birth control, coupled with shame-free sexual health education, universal healthcare and a generous social safety net, is also the best way to prevent abortion – the countries with the lowest abortion rates in the world all employ that simple model. You would think that if pro-life groups actually cared about babies and mothers, they would be pushing for everyone to have healthcare. You would think they would support things like well-baby care, and daycare funding, and federal parental leave, and aid to low-income families with dependent children. You would think that if pro-life groups were genuinely interested in lowering the abortion rate, they would be singing birth control's praises, and trying to make it as accessible and affordable as possible.

And yet the legislators who are the most hostile to funding children's health and who are the most hostile to widespread healthcare and education are consistently"pro-life". Pro-life groups rarely come out in support of initiatives that actually help born babies or pregnant women. And not a single US pro-life group supports birth control access. Not one. Many either don't take a position on it or are actively hostile to its use.

That's where personhood amendments come in.

The purpose of personhood amendments is to outlaw many forms of birth control, in addition to abortion. The amendments are failing at the ballot box, because even pro-life voters tend to like their contraception. But they may be succeeding in laying the groundwork to eventually deny birth control access. And they're doing it by redefining the basic science of birth control, and the facts of human reproduction.

The personhood amendments are notable because they define personhood as beginning at fertilisation – the moment sperm hits egg. At that moment, they say, a person is formed, and that person should have all of the rights and liberties afforded to any other citizen of the United States (a position that lends itself to all sorts of absurdities, but that's for another column). That's a major departure from how the scientific community has even defined pregnancy. Because it's awfully difficult to tell the exact moment an egg is fertilised – it can be days after sex – and since most fertilised eggs are naturally flushed out of the body and don't ever turn into babies, the medical community has defined the beginning of pregnancy as when the fertilised egg actually implants in the uterus, which can be a full week after intercourse. As far as definitions go, it's a pretty logical one.

In fact, if a woman isn't on hormonal birth control and is ovulating, more than half of any eggs that get fertilised naturally don't implant and are flushed out with her menstrual period. So it's actually more likely that a woman not on birth control who is sexually active is underwriting more egg "deaths" than a woman on the pill.

But, of course, egg deaths aren't the point. Pro-lifers don't actually believe that a fertilised egg is the moral equivalent of a newborn baby – if they did, there would certainly be major pushes for research on why more than half of all these cellular human beings are flushed out of the body and die. (Imagine if more than half of all three-year-olds suddenly dropped dead – we wouldn't just shrug our shoulders and say, "Well that's nature!") What they do believe is that birth control has given women too much freedom. And they realise that if they can change the terms of the debate – just as they did when they rebranded an embryo as a baby – they might make some headway in the long run.

Enter personhood amendments. It's a great strategy: you say that birth control kills fertilised eggs, then you try to pass a law that would make killing fertilised eggs murder, and then your opponents (logically) respond by pointing out that the proposed law is purposed to outlaw many forms of birth control. Voilà, you've just made the fantasy that birth control kills fertilised eggs a political truth. The Mississippi personhood amendment might have lost, but the anti-choice pseudo-science machine had a big win.

You can bet that personhood amendments will continue to pop up for this exact reason – redefining the terms of the debate, making up facts and obscuring their real agenda is how the anti-choice movement has always succeeded. It's how they have convinced millions of Americans that being pro-life has anything to do with caring about babies.

Birth control pills are not responsible for the mass slaughter of fertilised eggs. The idea that a fertilised egg should have all of the same rights and privileges as an adult man (and, apparently, greater rights than a living, breathing woman) is beyond ridiculous. But saving the "lives" of eggs was never the point.

Taking us back to a time where pregnancy was a punishment for sex (instead of a welcome and wanted event, which is the pro-choice ideal), and where women are primarily defined by their reproductive capacity, are the end goals. Part and parcel to that is outlawing not just abortion, but birth control, which is difficult in a country where most women use birth control. Opposition to abortion has already been successfully framed as being about "life", so birth control gets summarily jammed into the "life" framework, scientific fact be damned.

If we allow anti-choice groups to continue defining the terms of the debate, and if we take seriously their claims that personhood initiatives are about "life" and not actually about trying to control women's bodies and sex lives, it won't matter how many times the initiatives are defeated – the real losers will be women. And women will share that honor with men, children and social progress generally. It's going to be all of us.